1891.] 



255 



much like whalebone, with the fibres at right angles to the long axis of the knife. 

 The whalebone tissue is not continued quite to the end, but terminates just where 

 the plate gets rounded off to form the lancet-like head, its place hero being taken 

 by ordinary homogeneous chitino. So far there is nothing to distinguish it funda- 

 mentally from the ovipositor of A. viridella, but if we turn it over and examine the 

 under-side, a most unexpected and puzzling state of things presents itself, for we 

 find attached there a pair of supplementary knives, the counterparts of the main 

 ones. They lie, however, so directly under the latter, and match thorn so exactly, 

 that they are apt at first to be overlooked, whilst the structures 

 that do catch the eye are a pair of black chitinous spurs on 

 cither side, united by a common fibrous attachment to the 

 under-side of their respective rods at the junction of these with 

 the sub-plates. I will deal with these spurs first. Each pair 

 lies in the same vertical plane as its rod, but its component 

 parts face in opposite directions. The inner and shorter 

 spur (Fig. 11, e) looks towards the abdomen, and receives 

 numerous muscular fibres that come from some point within 

 the body. The precise spot I have not been able to ascertain* — 

 a matter of not so much consequence, since there can be no 

 question that the muscle is a retractor, and in conjunction with 

 the one on the opposite side withdraws the knife within the 

 body, and is, therefore, the retractor of the ovipositor. The 

 outer spur (Fig. 11, d) is longer, and faces outwards. Its 

 point is dark and chitinous, but its body is hyaline and apparently fibrous, indicating 

 that it is more pliant and mobile than the inner spur. Among my earlier notes is 

 one assigning a muscle to the point of this spur also, but as I have no preparation 

 by me that actually shows it, it may be that in those early dissections membrane 

 was mistaken for muscle, an error that might easily have happened. Yet after all I 

 believe that the observation was right, because the mechanism of the parts, as I 

 understand it, requires that such a muscle should exist. f But of this presently. 



Fio. 10. 



V 



Now, from the outer spurs, midway between their point and base, there comes 



Fio. 10.— Upper surface of knife-plate, with parts of the inner rods attached to it. 



Fiu. 11.— Side view of one-half oi knife-plate, aud its rod. a. Back of main knife. li, Back of 



supplementary knife. c, c', Whalebunc plates of main aud suiiplomentary knive.K. 



d, Lower spur, e, Upijer spur, with torn fibres of retractor muscle attached to it. 



f, Ventral sub-plate of ovipositor. 



* This point has since been cleared up, and the muscle found to arise from the point of the 



outer rod. 



t I have now ascertained that these muscles do exist. The arise, like the retractors of the 

 ovipositor, from the points of the outer rods, and end in extraordinarily long tendons, which are 

 inserted into the points of the outer .spurs. The jiresence of the tendons is most unusual, and 1 

 know no other instance of their occurrence. The consequent curtailment in length of the con- 

 tractile p.irts indicates that the muscles act within comparatively narrow limits— a circumstance 

 still further coutirmatory of the view, given later on, of the mechani.sm of the parts. 



